The present invention relates generally to the detection of the position or state of a moving object, preferably the detection of the position of an object moving within a body, such as for example the position of an organ or a tumor within a patient. The invention relates especially to image sequence matching for respiratory state detection, which can be used for extracranial radiosurgery.
The invention relates also to the determination of the respiratory state by matching a pair or series of x-ray images, which are for example taken during free-breathing, to a corresponding 4D volume scan.
To apply radiosurgical methods to tumors in the chest and abdomen, it is necessary to take into account respiratory motion, which can move the tumor by more than 1 cm. It is known to use implanted fiducials to track the movement of the tumor.
It is also known to track the movement of tumors without implanted fiducials. Reference is made to K. Berlinger, “Fiducial-Less Compensation of Breathing Motion in Extracranial Radiosurgery”, Dissertation, Fakultät für Informatik, Technische Universität München; K. Berlinger, M. Roth, J. Fisseler, O. Sauer, A. Schweikard, L. Vences, “Volumetric Deformation Model for Motion Compensation in Radiotherapy” in Medical Image Computing and Computer-Assisted Intervention-MICCAI 2004, Saint Malo, France, ISBN: 3-540-22977-9, pages 925-932, 2004 and A. Schweikard, H. Shiomi, J. Fisseler, M. Dötter, K. Berlinger, H. B. Gehl, J. Adler, “Fiducial-Less Respiration Tracking in Radiosurgery” in Medical Image Computing and Computer-Assisted Intervention-MICCAI 2004, Saint Malo, France, ISBN: 3-540-22977-9, pages 992-999, 2004.
U.S. Pat. No. 7,260,426 B2 discloses a method and an apparatus for locating an internal target region during treatment without implanted fiducials. The teaching of U.S. Pat. No. 7,260,426 B2 with respect to a radiation treatment device, as illustrated in FIG. 1 of U.S. Pat. No. 7,260,426 B2, and with respect to a real-time sensing system for monitoring external movement of a patient, is herewith included in this application.
U.S. application Ser. No. 10/652,786 discloses an apparatus and a method for registering 2D radiographic images with images reconstructed from 3D scan data.
It is known to place external markers, such as IR-reflectors or IR-emitters, on a patient. The markers can be tracked automatically with known optical methods at a high speed to obtain a position signal, which can for example be a breathing signal or a pulsation signal, being indicative of for example the respiratory state.
However, the markers alone cannot adequately reflect internal displacements caused for example by breathing motion, since a large external motion may occur together with a very small internal motion, and vice versa.